This program entitled "DNA Transactions and Aging" consists of an interrelated set of six projects directed by Drs. Paul Berg, Ronald W. Davis, David S. Hogness, Dale Kaiser, Arthur Kornberg and Robert Lehman. The program focuses on DNA transactions that we think are relevant to aging because they either cause or prevent alterations in a cell's repertoire of genetic functions. The rate at which such genetic errors accumulate in cell populations is clearly important to any consideration of the aging problem and, of course, that rate is determined by the interplay between these causative and preventive transactions. The program encompasses two areas of concentration within this central theme. One of these concerns the transposable DNA elements that move about the genome and generate mutational rearrangements in the chromosomal DNA. The other concerns those transactions that repair damage to the chromosomal DNA and regulate the fidelity of DNA replication.